Portable computers, or laptop computers as they are also called, are easily transportable computers that operate from either an external power source in a base operating mode, or a portable power source in a portable operating mode. External power sources are generally electrical outlets that have a supply of alternating current (AC) power, while portable power sources are generally rechargeable batteries that are housed in the computer. The processor is coupled to one or more input devices, such as a key board or mouse, and output devices, such as a printer or display unit. In use, an operator generally inputs data to the processor through the input devices, and the output devices visually present to the operator the data generated by the processor.
One objective of portable computers is to maintain an adequate processor operating rate for running software applications. Processor manufacturers continually develop faster, more powerful processors as measured by the number of calculations that may be performed in a second. In general, more powerful processors consume more electrical energy and produce more heat energy than earlier generations of slower processors. For example, the more powerful Intel.RTM. Pentium Pro processor consumes approximately 23.2-31.7 W of power, while the slower Intel.RTM. 486 processor only consumes about 1.4W-6W of power. As a result, more powerful processors produce more heat than slower processors. One difficulty in using more powerful processors is that their operating temperatures increase with increasing operating speed. Thus, high speed portable computers generally have cooling systems that dissipate heat from the processors.
Conventional cooling systems in computers are typically active cooling systems that consume power, or a combination of active cooling systems and passive cooling systems. Examples of active cooling systems include electrical fans that blow air across the processor, or thermoelectric heat pumps that draw heat away from the processor. Passive cooling systems are generally heat sinks attached to the processor to increase the surface area over which heat dissipates from the processor.
One general problem created by more powerful processors is that their high power consumption significantly reduces the period during which a portable computer can operate from its portable power source. The high-powered processors not only consume more power themselves, but the conventional cooling units on the portable computers also consume more power to dissipate the additional heat generated by the processors. Therefore, to increase the period during which the computer can operate from its portable power source, it is generally desirable to reduce the rate at which the computer components consume power from the portable power source.
A more specific problem of conventional active cooling systems is that they continuously operate and consume power throughout the operation of the computer. Since the new, more powerful processors consume even more power than earlier generations of processors, continuously operating the cooling unit further reduces the period that a computer can operate from its portable power source. Thus, it would be desirable to develop a cooling system that conserves power when the computer operates from its portable power source.
Another problem of conventional cooling systems is that their size and weight generally reduce the portability of portable computers. Yet, an important aspect of portable computers is minimizing their size and weight to make them easier to carry and store. Thus, it would also be desirable to develop a cooling system that enhances the portability of portable computers.